When Timing Matters: Effects of Maternal Separation and Post-Weaning High-Fat Diet on Liver Morphology in a Rodent Model

<b>Background</b>: Early-life stress and dietary habits are key determinants of metabolic health. This study investigates the combined effects of maternal separation (MS) and a post-weaning high-fat diet (HFD) on liver morphology in male C57BL/6 mice. <b>Methods</b>: Male mice were subjected to MS during early postnatal life or kept unmanipulated (UM). After weaning, animals were assigned to either a control diet (CD) or an HFD, forming four groups: UM-CD, UM-HFD, MS-CD, and MS-HFD. Liver histology, collagen deposition, and both morphometric and stereological parameters were assessed following 16 weeks of dietary intervention. <b>Results</b>: MS and HFD independently altered liver structure, while the combination of both factors intensified these changes. The MS-HFD group exhibited pronounced steatosis, mixed inflammatory infiltrates, and hepatocellular ballooning, with a significantly higher NAFLD Activity Score (NAS). No significant differences were observed in liver fibrosis. Morphometric analysis revealed increased body mass in HFD-fed groups and elevated liver mass in MS-HFD. Liver volume was higher in MS-HFD, though not significantly. Liver stereology revealed reduced numerical density of hepatocytes (Nv_hep) and increased surface density (Sv_hep) in MS groups, with the most pronounced effects in MS-HFD. <b>Conclusions</b>: Maternal separation amplifies the hepatic alterations induced by HFD, promoting early inflammatory and steatotic changes. These findings highlight the significance of early-life stress as a factor increasing susceptibility to diet-induced liver damage.